Apparatus for preventing reverse rotation for hydraulic actuator

ABSTRACT

A reverse rotation preventing apparatus for a hydraulic actuator includes a hydraulic actuator for driving an inertia member, a main valve which is switched to a driving position in which a pressure oil is supplied to one of first and second ports of the hydraulic actuator and another one thereof is communicated with a tank and to a neutral position in which the first and second ports are shut off, a relief valve adapted to flow out a pressure oil in the first or second port to the tank at a time when a pressure on the side of the first or second port is higher than a set high pressure, a suction valve adapted to suck the pressure oil to the first or second port at a time when the pressure on the side of the first or second port is negative, and a reverse rotation preventing valve adapted to communicate the first and second port sides with the tanks respectively at a time when the pressure on the sides of the first and second ports is higher than a set pressure which is a pressure lower than the set high pressure.

TECHNICAL FIELD

The present invention relates to an apparatus for preventing reverserotation of a hydraulic motor driving an inertia member (an objecthaving a large inertia) such as a swing hydraulic motor for swinging anupper revolving member of a power shovel or a cylinder for swinging anarm or boom.

BACKGROUND ART

When a hydraulic motor for driving an inertia member is stopped, firstand second main circuits connected to first and second ports of thehydraulic motor are shut off by brake valves. However, in such case,since the hydraulic motor is rotated by an inertia force of the inertiamember to thereby cause a pumping function which causes a cavitation toone of the first and second main circuits, the first and second maincircuits are communicated through a relief valve so that a pressure oildrained from one of the ports flows, through the pumping function of thehydraulic motor, to the other one of the ports to smoothly stop thehydraulic motor.

However, when the hydraulic motor is stopped by the manner mentionedabove, an elastic energy is stored to a connection shaft connecting thehydraulic motor and the inertia member at the hydraulic motor stoppingtime, the hydraulic motor is reversely driven by the elastic energy, andthe hydraulic motor is then stopped through the repetition of suchoperation. That is, a reverse rotation phenomenon due to reaction orrebound force caused at this time is generated, this phenomenon beingcalled herein a rebound reverse rotation phenomenon.

For the reason described above, for example, as disclosed in JapanesePatent Laid-open Publication No SHO 57-25570, there is provided areverse rotation preventing apparatus for preventing the rebound reverserotation phenomenon by disposing reverse rotation preventing valves tothe first and second main circuits, respectively, in a manner that whena pressure in one of the main circuits exceeds a preset pressure, a highpressure oil flows to the other one of the main circuits.

According to such reverse rotation preventing apparatus, since the highpressure oil in one of the main circuits is merely drained to the otherone thereof, much time is taken up to the time when the pressures in thefirst and second main circuits are lowered, and hence, much time is alsotaken up to the time when the rebound reverse rotation phenomenon issettled. That is, the hydraulic motor is much reversely rotated till theoperation of the hydraulic motor stops.

As mentioned above, the fact that much time is taken up to the settlingof the rebound reverse rotation phenomenon means that much time is alsotaken up from the starting of the hydraulic motor stopping operation tothe actual stopping thereof. Accordingly, when applied to a hydraulicpower shovel, a time interval required from the swinging time of theupper revolving member to an excavation starting time is made long,lowering a working efficiency.

Therefore, the present invention aims to provide an apparatus forpreventing a reverse rotation of a hydraulic actuator capable of makingshort a time interval up to the settling of the rebound reverse rotationphenomenon when a hydraulic actuator such as hydraulic motor is operatedto stop the same.

DISCLOSURE OF THE INVENTION

To achieve the above object, according to one embodiment of the presentinvention, there is provided a reverse rotation preventing apparatus fora hydraulic actuator comprising: a hydraulic actuator for driving aninertia member; a main valve which is switched to a driving position inwhich a pressure oil is supplied to one of first and second ports of thehydraulic actuator and another one thereof is communicated with a tankand to a neutral position in which the first and second ports are shutoff; a relief valve adapted to flow out a pressure oil in the first orsecond port to the tank at a time when a pressure on the side of thefirst or second port is higher than a set high pressure; a suction valveadapted to suck the pressure oil to the first or second port at a timewhen the pressure on the side of the first or second port is negative;and a reverse rotation preventing valve adapted to communicate the firstand second port sides with the tanks respectively at a time when thepressures on the sides of the first and second ports are higher than aset pressure which is a pressure lower than the set high pressure.

According to the above structure, the high pressure oils on the firstand second port sides are directly flowed out to the tanks on anoccurrence of a rebound reverse rotation phenomenon of the hydraulicactuator by the elastic energy at a time of stopping the operation ofthe hydraulic actuator, so that the pressures on the first and secondport sides can be lowered in a short time and the rebound reverserotation phenomenon can be settled in a short time.

In addition to the above structure, it is desired to dispose a delaymeans such as throttle for delaying flow-out of the pressure oil to acircuit means communicating the first and second port sides respectivelyto the tanks by the reverse rotation preventing valve.

Furthermore, it may be possible to dispose a change-over valve servingto cause flow-out of the high pressure oil on the first and second portsides in a case of a pressure higher than another set pressure.

Furthermore, it may be possible to dispose a second delay means such asthrottle or combination of a throttle and a check valve for delayingchange-over time from a communication position to a shut-off position ofthe reverse rotation preventing valve to a circuit means for controllingcommunication and shut-off of the reverse rotation preventing valve.

Still furthermore, it is desired that the reverse rotation preventingvalve is composed of first and second valves which are communicated andshut off respectively by pressures on the first and second port sides.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more understandable from the followingdetailed description and accompanying drawings representing embodimentsof the present invention. Further, it is to be noted that theembodiments shown in the accompanying drawings do not intend to specifythe invention and merely intend to make easy the understanding of theinvention.

In the accompanying drawings:

FIG. 1 is a hydraulic circuit diagram including a first embodiment of anapparatus for preventing reverse rotation of a hydraulic actuatoraccording to the present invention.

FIG. 2 is a hydraulic circuit diagram including a second embodiment ofan apparatus for preventing reverse rotation of a hydraulic actuatoraccording to the present invention.

FIG. 3 is a hydraulic circuit diagram including a third embodiment of anapparatus for preventing reverse rotation of a hydraulic actuatoraccording to the present invention.

FIG. 4 is a hydraulic circuit diagram including a fourth embodiment ofan apparatus for preventing reverse rotation of a hydraulic actuatoraccording to the present invention.

FIG. 5 is a hydraulic circuit diagram including a fifth embodiment of anapparatus for preventing reverse rotation of a hydraulic actuatoraccording to the present invention.

FIG. 6 is a sectional view of an important portion of the fifthembodiment.

FIG. 7 is a hydraulic circuit diagram including a sixth embodiment of anapparatus for preventing reverse rotation of a hydraulic actuatoraccording to the present invention.

FIG. 8 is a hydraulic circuit diagram including a seventh embodiment ofan apparatus for preventing reverse rotation of a hydraulic actuatoraccording to the present invention.

PREFERABLE MODES FOR EMBODYING THE INVENTION

Hereunder, an apparatus for preventing reverse rotation of a hydraulicactuator according to the present invention will be described withreference to the accompanying drawings.

FIG. 1 represents the first embodiment. This embodiment has a structuresuch that first and second main circuits 5 and 6 are connectedrespectively to first and second ports 3 and 4 of a hydraulic actuator,such as hydraulic motor 2, for rotating an inertia member 1 and thecommunication between the first and second main circuits 5 and 6 and adrain passage 7a of a hydraulic pump 7 and a tank 8 is established orshut off by means of a main valve 9.

The main valve 9 takes a neutral position A at which the drain passage7a is communicated with the tank 8 and the first and second maincircuits 5 and 6 are shut off, a first position B at which the drainpassage 7a is communicated with the first main circuit 5 and the secondmain circuit 6 is communicated with the tank 8, and a second position Cat which the drain passage 7a is communicated with the second maincircuit 6 and the first main circuit 5 is communicated with the tank 8.The main valve 9 is changed over to the respective positions by means ofan operation lever 10.

Further, the main valve 9 may take a structure in which the drainpassage 7a is shut off or communicated with another circuit at theneutral position A of the main valve 9. Furthermore, the main valve 9may also have a structure, such as disclosed in Japanese Utility ModelLaid-open Publication No. SHO 57-112102, in which the first and secondmain circuits 5 and 6 are communicated with the tank 8, and in thisstructure, a counterbalance valve may be provided between the first andsecond main circuits 5 and 6. That is, there may be arranged means forcarrying out a change-over operation between a drive condition in whicha pressure oil is supplied to one of the first and second ports 3 and 4of the hydraulic motor 2 and the other one of the ports is communicatedwith the tank 8 and a neutral condition in which the first and secondports 3 and 4 are shut off.

In the first main circuit 5, a first relief valve 11 and a first suctionvalve 12 are connected so that the pressure in the first main circuit 5does not exceed a set pressure of the first relief valve 11 and, at atime when an inner pressure of the first main circuit 5 becomesnegative, an oil in the tank 8 is sucked through the first suction valve12 to thereby prevent the creation of the negative pressure in the firstmain circuit 5.

In the second main circuit 6, a second relief valve 13 and a secondsuction valve 14 are connected so that the pressure in the second maincircuit 6 does not exceed a set pressure of the second relief valve 13and, at a time when an inner pressure of the second main circuit 6becomes negative, an oil in the tank 8 is sucked through the secondsuction valve 14 to thereby prevent the creation of the negativepressure in the second main circuit 6.

A reverse rotation preventing valve 22 is composed of a first valve 20and a second valve 21. The first valve 20 is held to a shut-off positionD for shutting off first, second, third and fourth ports 23, 24, 25 and26 by means of a spring 27 to be capable of changing over to acommunication position E at which the first and second ports 23 and 24are communicated and the third and fourth ports 25 and 26 are alsocommunicated by means of a pressure of a pressure oil in a pressurereceiving chamber 28.

The second valve 21 is held to a shut-off position D for shutting offfirst, second, third and fourth ports 29, 30, 31 and 32 by means of aspring 33 to be capable of changing over to a communication position Eat which the first and second ports 29 and 30 are communicated and thethird and fourth ports 31 and 32 are also communicated by means of apressure of a pressure oil in a pressure receiving chamber 34. Thesecond valve 21 has substantially the same structure as that of thefirst valve 20.

The first port 23 of the first valve 20 is connected to the first maincircuit 5 and also connected to the pressure receiving chamber 28, thesecond port 24 thereof is connected to the fourth port 32 of the secondvalve 21, the third port 25 is connected to a first drain passage 35,and the fourth port 26 is communicated with the second port 30 of thesecond valve 21.

The first port 29 of the second valve 21 is connected to the second maincircuit 6 and also connected to the pressure receiving chamber 34, andthe third port 31 thereof is connected to a second drain passage 36.

According to the arrangement described above, the first and secondvalves 20 and 21 take their shut-off positions D at a time when thepressures P₁ and P₂ in the first and second main circuits 5 and 6 becomelower than a set pressure of, for example, 20 Kg/cm² and take theircommunication positions E at a time when the pressures become more thanthe set pressure.

The operation of the present embodiment will be described hereunder.

First, the main valve 9 is operated to take the first position B bywhich the drain pressure oil from the hydraulic pump 7 is supplied tothe first port 3 of the hydraulic motor 2 through the first main circuit5 and the second port 4 thereof is communicated with the tank 8 throughthe second main circuit 6. The hydraulic motor 2 is thereby rotated in aclockwise direction of the arrow a.

At this time, although the first valve 20 takes its communicationposition E with the pressure P₁ of the first main circuit 5, because thepressure P₂ of the second main circuit 6 is substantially zero, thesecond valve 21 takes its shut-off position, and accordingly, the firstand second valves 20 and 21 attain no function as reverse rotationpreventing valve means.

When the main valve 9 is then shifted to the neutral position A from thestate mentioned above, the first and second main circuits 5 and 6 areshut off and the hydraulic motor 2 is rotated in the direction of thearrow a by the inertia energy of the inertia member 1 and attains thepumping function. According to such operation, the pressure P₂ of thesecond main circuit 6 increases. However, in the case of large inertiaenergy, the pressure P₂ becomes more than the set pressure, for example,of 300 Kg/cm², of the second relief valve 13, and as a result, thepressure oil in the second main circuit 6 flows out into the tank 8through the relief function of the second relief valve 13, thus theinertia energy to absorbed.

In this moment, the second valve 21 takes its communication position E.However, because the pressure in the first main circuit 5 issubstantially zero, the first and second valves 20 and 21 attain nofunction as reverse rotation preventing valve means.

Thereafter, since the hydraulic motor 2 is subjected to a force to berotated in a direction reverse to the arrow direction a by the elasticenergy stored in the inertia member 1 and the connection shaft 15 of thehydraulic motor 2, the pressure P₂ in the second main circuit 6decreases and the pressure P₁ in the first main circuit 5 increases. Thehydraulic motor 2 is then stopped through the repetition of suchoperations. That is, it is said that the hydraulic motor 2 is stoppedwhile causing the rebound reverse rotation phenomenon.

When the rebound reverse rotation phenomenon is caused, the first andsecond valves 20 and 21 operate as the reverse rotation preventing valve22 to thereby early settle the rebound reverse rotation phenomenon.

The above operation will be mentioned in detail hereunder.

As mentioned above, when the pressure P₂ in the second main circuit 6increases through the pumping operation of the hydraulic motor 2, thesecond valve 21 takes the communication position E, and under the state,when the hydraulic motor 2 is reversely rotated by the elastic energymentioned above, the pressure P₁ in the first main circuit 5 increases.

According to this operation, the first valve 20 takes the communicationposition E and the first main circuit 5 is communicated with the seconddrain passage 36 through the first and second ports 23 and 24 of thefirst valve 20 and the fourth and third ports 32 and 31 of the secondvalve 21, and the high pressure oil in the first main circuit 5 flowsout into the tank 8. On the other hand, the second main circuit 6 iscommunicated with the first drain passage 35 through the first andsecond ports 29 and 30 of the second valve 21 and the fourth and thirdports 26 and 25 of the first valve 20, and the high pressure oil in thesecond main circuit 6 flows out into the tank 8. Through suchoperations, the elastic energy mentioned above is absorbed and therebound reverse rotation phenomenon can be early settle.

That is, since the reverse rotation preventing valve 22 serves so thatthe high pressure oils caused in the first and second main circuits 5and 6 flow out into the tanks 8 at the time of generating the reboundreverse rotation phenomenon, the pressures in the first and second maincircuits 5 and 6 decrease in an early stage to thereby early settle therebound reverse rotation phenomenon.

Further, during the operations mentioned above, if the pressure in thefirst or second main circuit 5 or 6 lowers below the set pressurenecessary for changing over the communication position E of the first orsecond valve 20 or 21, the first or second valve 20 or 21 immediatelytakes the shut-off position D to thereby stop the operation for flowingout the high pressure oil in the first and second main circuit 5 and 6into the tanks 8.

FIG. 2 represents the second embodiment of the present invention. Inthis embodiment, throttles 39 are provided respectively for a circuit 37communicating the second port 24 of the first valve 20 with the fourthport 32 of the second valve 21 and for a circuit 38 communicating thefourth port 26 of the first valve 20 and the second port 30 of thesecond valve 21.

According to this arrangement, since the high pressure oil in the firstand second main circuits 5 and 6 slowly flows out towards the tanks 8,the pressure in the main circuits 5 and 6 changes slowly, that is, thefirst and second valves 20 and 21 are slowly changed over, so that ahunting phenomenon is hardly caused.

The throttle(s) 39 may be provided for only one of the circuits 37 and38, for both or only one of the first and second drain passages 35 and36, or both or only one of the passages between the first and secondvalves 20 and 21 and the main circuits 5 and 6.

That is, it may be said that the throttle(s) 39 is provided for both orone of a portion through which the first main circuit 5 is communicatedwith the tank 8 and a portion through which the second main circuit 6 iscommunicated with the tank 8.

FIG. 3 represents the third embodiment of the present invention. In thisembodiment, a change-over valve 40 is disposed to a portion between thefirst and second drain passages 35 and 36 and the tank 8, and thechange-over valve 40 is held to a drain position F by a spring 41 andtakes a pressure oil supply position G by an external force such aspilot pressure oil, electromagnetic force, hand force, etc., therebysupplying the pressure oil from an auxiliary hydraulic pump 42 to thefirst and second drain passages 35 and 36. A relief valve 43 isconnected to a drain passage of the auxiliary hydraulic pump 42.

According to such arrangement, when the change-over valve 40 is shiftedto the pressure oil supply position G, the pressure oil having the setpressure of the relief valve 43 is supplied to the first and seconddrain passages 35 and 36. When the first and second valves 20 and 21take their communication positions E, the flow of the pressure oil fromthe first and second main circuits 5 and 6 to the first and second drainpassages 35 and 36 becomes worse, so that an operation for quicklysettling the rebound reverse rotation phenomenon is not performed.

FIG. 4 represents the fourth embodiment of the present invention. Inthis embodiment, the first and second main circuits 5 and 6 areconnected to the first port 3 opened to a first chamber 51 of a cylinder50 and the second port 4 opened to a second chamber 52 of the cylinder50, respectively, to make the cylinder expand or contract 50. Thethrottles 39 are disposed in the first and second valves 20 and 21.

FIG. 5 represents the fifth embodiment of the present invention. In thisembodiment, in addition to the arrangement of the first embodiment,throttles 53 and 54 are provided respectively for a circuit between thefirst port 23 of the first valve 20 and the pressure receiving chamber28 and for a circuit between the first port 29 and the pressurereceiving chamber 34. These throttles 53 and 54 are formed by circularspaces defined between outer peripheral surfaces of spools of the firstand second valves 20 and 21 and inner peripheral surfaces of spoolholes. These throttles 53 and 54 may be formed by orifices formed to thespools or housings of the first and second valves 20 and 21.

According to the arrangement mentioned above, at a time when the firstand second valves 20 and 21 return to their shut-off positions D fromthe communication positions E, these valves return slowly till the timewhen the pressure oils in the pressure receiving chambers 28 and 34 flowto the ports 23 and 29, respectively, so that the first and secondvalves 20 and 21 have the communication positions E for a long timeinterval, and accordingly, the time for flowing out the high pressureoil in the first and second main circuits 5 and 6 is lengthened, thusmore quickly lowering the pressures in the first and second maincircuits 5 and 6 to thereby more speedily settle the rebound reverserotation phenomenon.

The arrangement of the throttles 53 and 54 as in the present embodimenthas a simple and compact structure involving less cost in comparisonwith the arrangement of a slow return valve.

FIG. 7 represents the sixth embodiment of the present invention. In thisembodiment, in addition to the structure of the first embodiment, aportion in which the spring 27 of the first valve 20 is accommodated isconstructed as an oil chamber, a throttle 55 and a check valve 56 aredisposed between the oil chamber and the first drain passage 35, and athrottle 57 and a check valve 58 are disposed between the oil chamberand the second drain passage 36. According to such arrangement, at thetime when the first and second valves 20 and 21 return to their shut-offpositions D from their communication positions E, the oil flow towardsthe respective oil chambers becomes delayed, so that the switchingfunction from the communication positions E to the shut-off positions Dis also delayed, and as a result, the first and second valves 20 and 21stay much time in their switched communication positions E.

FIG. 8 represents the seventh embodiment of the present invention. Inthis embodiment, in addition to the structure of the first embodiment, athrottle 59 and a check valve 60 are disposed between the pressurereceiving chamber 28 and the first port 23 and a throttle 61 and a checkvalve 62 are disposed between the pressure receiving chamber 34 and thefirst port 29. According to this arrangement, at the time when the firstand second valves 20 and 21 return to their shut-off positions D fromtheir communication positions E, the oil flow from the pressurereceiving chambers 28 and 34 to the respective oil chambers becomesdelayed, so that the switching from the communication positions E to theshut-off positions D is also delayed, and as a result, the first andsecond valves 20 and 21 stay much of the time in their switchedcommunication positions E.

Further, it is to be noted that any combination of either one of thesecond, fourth, fifth, sixth and seventh embodiments with the thirdembodiment is possible. Furthermore, it is possible to combine thesecond or fourth embodiment with either one of the fifth, sixth andseventh embodiments.

As mentioned hereinbefore, according to the reverse rotation preventingapparatus of the hydraulic actuator of the present invention, when therebound reverse rotation phenomenon is caused to the hydraulic actuatorby the elastic energy at a time of the stopping of the operation of thehydraulic actuator, the high pressure oils on the first and second portsides directly flow into the tanks, so that the pressures on the firstand second port sides are lowered in a short time period and the reboundreverse rotation phenomenon can be settled in a short time period.

Further, it is self-evident to a person skilled in the art that althoughthe present invention is described hereinbefore with reference to theexemplary embodiments, it is possible to make various changes, deletionsand additions to the disclosed embodiment without departing from thesubject and scope of the present invention. Accordingly, it is to beunderstood that the present invention is not limited to the describedembodiments and includes scopes or its equivalent scope defined by theelements recited in the appended claims.

What is claimed is:
 1. A reverse rotation preventing apparatus for ahydraulic actuator comprising:a hydraulic actuator for driving aninertia member; a main valve which is switched to a driving position inwhich a pressure oil is supplied to one of first and second ports of thehydraulic actuator and another one thereof is communicated with a tankand to a neutral position in which said first and second ports are shutoff; a relief valve adapted to flow out a pressure oil in said first orsecond port to the tank at a time when a pressure on the side of saidfirst or second port is higher than a set high pressure; a suction valveadapted to suck the pressure oil to said first or second port at a timewhen the pressure on the side of said first or second port is negative;and a reverse rotation preventing valve adapted to communicate saidfirst and second port sides with the tanks respectively at a time whenthe pressure on the sides of said first and second ports is higher thana set pressure which is a pressure lower than said set high pressure. 2.A reverse rotation preventing apparatus for a hydraulic actuatoraccording to claim 1, wherein a first delay means for delaying flow-outof the pressure oil is provided for a circuit means communicating saidfirst and second port sides respectively with the tanks by said reverserotation preventing valve.
 3. A reverse rotation preventing apparatusfor a hydraulic actuator according to claim 2, wherein said first delaymeans is a throttle.
 4. A reverse rotation preventing apparatus for ahydraulic actuator according to claim 1, wherein a change-over valve isprovided for serving to cause flow-out of the high pressure oil on saidfirst and second port sides in a case of a pressure higher than anotherset pressure.
 5. A reverse rotation preventing apparatus for a hydraulicactuator according to claim 2, wherein a change-over valve is providedfor serving to cause flow-out of the high pressure oil on said first andsecond port sides in a case of a pressure higher than another setpressure.
 6. A reverse rotation preventing apparatus for a hydraulicactuator according to any one of claims 1 to 5, wherein a second delaymeans for delaying change-over from a communication position to ashut-off position of said reverse rotation preventing valve is providedfor a circuit means for controlling communication and shut-off of thereverse rotation preventing valve.
 7. A reverse rotation preventingapparatus for a hydraulic actuator according to claim 6, wherein saidsecond delay means is a throttle.
 8. A reverse rotation preventingapparatus for a hydraulic actuator according to claim 6, wherein saidsecond delay means is a combination of a throttle and a check valve. 9.A reverse rotation preventing apparatus for a hydraulic actuatoraccording to any one of claims 1 to 5, wherein said reverse rotationpreventing valve is composed of first and second valves which arecommunicated and shut off respectively by pressures on the first andsecond port sides.